This invention relates to fenders or bumpers having elastomeric resilient means such as rubber or polyethylene, which are used to fend or prevent excessive shock on bumping, collision or contact of two bodies, such as between a truck and a loading dock, a boat and a pier or wharf, a towboat and a barge, or other moving or converging bodies, the fenders being attached to one or both of the bodies. In particular, the invention relates to bumpers or fenders for absorbing shearing forces induced into marine fender/vessel contact surfaces rather than having the forces imposed on the contact surface attaching hardware.
Shearing forces are the sum of forces caused by friction, direct engagement by hull projection and cold flow caused by high contact pressure. These shearing forces occur both vertically and horizontally. When two bodies converge together, the shearing forces created may damage the contact surfaces of either of the converging bodies.
To prevent damage to either of the converging bodies, fenders or bumpers have been used to absorb the shearing forces induced in the contact surfaces. Typically, these fenders have been attached to the supporting structure by either bolts threaded into tapped holes in the supporting structure or nuts screwed into studs welded onto the support structure.
However, several drawbacks are associated with these fenders. Tapped holes in the supporting structure create points for stress concentrations and corrosion. This often leads to damage to the supporting structure. In addition, the smaller cross-sectional area of the bolts or studs cannot sufficiently absorb the shearing forces. Consequently, the fender may be sheared off at the support structure under high shear loads. Moreover, the smaller diameter of the bolts or studs causes the fender contact surface surrounding the bolts or studs to deform around the bolts or studs under high shear loads. At times, deformation may be large enough to cause the fender to become unattached from the supporting structure.
Another type of fender which has been commonly used is a bumper which includes parallel bars or rails which are welded to the supporting surface. These bars typically have tapped holes into which bolts are threaded. With these fenders, the bumper pad or elastomeric material has a portion which is captured between the head of the bolt and the rail or bar. Because the fender rails run continuously in one direction, the rails absorb shear forces and prevent movement in only one direction, perpendicular to the rails. Because only the bolts themselves pass through the bumper pads or the elastomeric fender material, the bolts must absorb all the shear forces in the direction parallel to the rails. Consequently, these fenders require very high strength bolts.
Another drawback to this type of fender is that all the forces are concentrated at the rails. As a result, the rails may become deformed or may become unattached from the supporting surface.